Graham Mackrell, managing director Harmonic Drive, explains why its strain wave gears have been the top choice in space for over forty years.

Anything that goes into space is seen as the pinnacle of human creation. Astronauts are highly trained and are at the peak of physical fitness, space shuttles are crafted by large teams of expert engineers and all the technology used is so high-tech it’s as if it belongs to science fiction.

Driving on Mars!

Many decades ago, the first Harmonic Drive gears were sent into space during the Apollo 15 mission. Even from the beginnings of the space race, the expectations for the technology used were high. The equipment used in space had to be reliable, compact and lightweight and given the increasing demands on equipment in today’s space missions, it must also now be highly accurate with zero backlash and have high torque capacity.

When aerospace engineers were recently designing a new space rover, they looked to Harmonic Drive gears for reliability. Due to the obvious difficulties of performing repairs in space, a high mean time between equipment failures is a high priority. Harmonic Drive products achieve this by prioritising quality throughout the entire design and manufacturing process.

It is vital that aerospace gears are thoroughly tested before they are sent to customers, ensuring that they always receive a quality product. At Harmonic Drive, we test products using finite element method (FEM) testing. This process simulates real world physics to ensure that the product is capable of surviving in space. For example, structural testing is carried out to ensure the product is robust and the space rover travelling over rough terrain will not damage the actuators used in the wheels. Thermodynamic properties are also important as aerospace gears are often exposed to both extremes of the temperature range, which are tested in the initial design process.

Also considered in the design process is the part count of the aerospace gears. Harmonic uses a low part count which means that they are maintenance free. In addition, there is a lower chance of components failing giving the gears a high Mean Time Between Failure (MTBF). This also contributes to the compactness and light weight of the gears, a feature essential in space.

Another key feature for aerospace gears is high torque capacity and zero backlash. This is essential for systems which communicate the location of the rover to the control room. If traditional, high backlash gears were to be used, the system would misreport the rover’s location. This would cause problems when the rover is used to survey uncharted areas of planets and could lead to inaccurate mapping. Due to the emphasis on high precision with Harmonic Drive gears, this problem can be avoided.

The numerous quality processes that Harmonic Drive undertakes have led to recognition from a number of accrediting bodies. Harmonic Drive products are AS9100 certified, a specific aerospace standard for the design, manufacture and sale of precision gear reducers, servo-actuators and electro-mechanical positioning systems.

To be the pinnacle of global technology, there are no shortcuts. Components used in aerospace technology must be subject to vigorous testing in order to be reliable, safe and have a long product life.

@HarmonicDriveUK #PAuto #Robotics @StoneJunctionPR

When the European Space Agency’s (ESA) Rosetta space probe arrived at Comet 67P/Churyumov-Gerasimenko it had been travelling for ten years and had travelled 4 billion miles on just one tank of fuel. If the fuel had run out before the probe reached the comet, the navigational thrusters would not have been able to make the numerous course corrections needed to rendezvous with the comet and then establish a stable orbit from which to launch the Philae landing module.

Throughout the long journey, Kistler pressure sensors monitored the fuel consumption continuously for the whole ten years to ensure that Rosetta arrived at its destination with enough fuel to make the final corrections to put the probe into orbit.

The Rosetta mission was one of the most ambitious projects executed by the ESA and two Kistler piezoresistive sensors played a small but valuable part in the success of the project by providing precision fuel monitoring from March 2004 onwards.

Sensor in space!

The key selection criteria for these sensors included their proven longevity and total reliability despite high levels of vibration at lift-off and years of zero gravity conditions. Rosetta’s cargo includes what is known as the Rosetta Disk – a nickel alloy disk with information etched onto it in image form. The disk contains about 13,000 pages of text in 1200 different languages, and it should still be readable after 10,000 years: durable though they are, even Kistler’s sensors are unlikely to be functioning after such a lengthy period!

FTIR gas analysis in the testing of satellite launch systems and on board satelite

Europe’s leading space technology company Astrium, has employed a sophisticated portable FTIR gas analyser as part of a test programme for satellite launch systems. The analyser, a ‘Gasmet DX4030‘, was supplied by instrumentation specialist Quantitech.

Astrium Propulsion Test & Launch Services Manager, Greg Richardson, says: “Many of the satellites that we design, build and launch are worth millions of Euros, so our test methods have to be extremely rigorous.

“The DX4030 was chosen because of its ability to provide highly accurate results for almost any gas. However, its intuitive software, compact size and portability were significant considerations because we use the technology at a number of our locations around the world.”

One of the tests that are performed on the propulsion systems is to check the integrity of the chambers that contain rocket fuel. To achieve this, the tanks are filled with a simulant (often isopropyl alcohol and demineralised water) and exposed to launch simulation conditions – pressure, heat, vibration etc. The simulant is then removed and the DX4030 is used to check for contamination or leaks.

LISA Pathfinder

The DX4030 was first utilised in the testing of the LISA Pathfinder; a project for which Astrium was selected by the European Space Agency to build and launch a spacecraft that will be packed with radical instrumentation and technology to pave the way for LISA (Laser Interferometer Space Antenna), the world’s first space-based gravity wave detector which will open a new window on the Universe by measuring gravitational waves generated by exotic objects such as collapsing binary star systems and massive black holes. In doing so, this project will be able to test a phenomenon predicted by Einstein’s General Theory of Relativity in 1916.

Star census
The analyser has also been used in testing the Gaia satellite which will conduct a census of a thousand million stars in our Galaxy, monitoring each of its target stars about 70 times over a five-year period. Gaia will precisely chart their positions, distances, movements, and changes in brightness. It is expected to discover hundreds of thousands of new celestial objects, such as extra-solar planets and failed stars called brown dwarfs. Gaia should also observe hundreds of thousands of asteroids within our own solar system.

DX 4040 with PDA

The DX4030 employs FTIR gas detection technology to obtain infrared spectra by first collecting an ‘interferogram’ of a sample signal with an interferometer, which measures all infrared frequencies simultaneously to produce a spectrum. This means that data is collected for the required parameters in addition to spectra for almost all others.

Commenting on the work at Astrium, Quantitech’s Dr Andrew Hobson said: “This has to be one of the more unusual applications for the DX4030. It is more commonly used for chemical spill, security and forensic investigations, and for occupational health, anaesthetic gas monitoring and research. The same technology is also employed to monitor industrial processes and gaseous emissions. However, Astrium’s work clearly demonstrates the flexibility of the device and we are delighted to have been involved.”